We evaluated the loss of sensitivity due to the motion experienced by a hull-mounted transducer and its effects upon the estimated biomass of southern blue whiting (Micromesistius australis) in an acoustic survey conducted in the southeastern Pacific, off the Chilean coast, during the austral winter of 2009. Vessel motion data (pitch and roll) were registered in situ using a digital clinometer and used to correct the nautical area scattering coefficients (NASC) in elementary sampling units of 926 m distance by 10 m depth. These NASC correction factors (NASCcp) were calculated using Dunford's algorithm for circular transducers. We found high variability in NASCcp, which averaged 12%, and ranged between 0 and 50%. NASCcp variability was explained significantly by the mean depth of the integrated stratum (33%), the weather condition, as measured by Beaufort's scale (5%), and the vessel course relative to wind direction (2%). The empirical model we used to explain NASC Cp variability may be suitable for correcting bias due to transducer motion in other, past and future, fisheries acoustic surveys targeting mid-water species under rough weather conditions.

Se evaluó la pérdida de sensibilidad producida por el movimiento de un transductor montado en el casco y sus efectos sobre la abundancia y biomasa estimada de merluza de tres aletas (Micromesistius australis) en un estudio acústico realizado en el Pacífico suroriental, frente a la costa de Chile, durante el invierno austral de 2009. Los datos de movimiento del barco (cabeceo y balanceo) fueron registrados in situ utilizando un clinómetro digital y luego utilizados para estimar la pérdida teórica de sensibilidad del transductor y, finalmente, traducir esta pérdida en factores de corrección del coeficiente de dispersión por área náutica (NASC) calculados para intervalos básicos de muestreo de 926 m de distancia por 10 m de profundidad. Los factores de corrección del NASC (NASC Cp) fueron calculados utilizando el algoritmo de Dunford para transductores circulares. Los valores estimados del NASCCp presentaron gran variabilidad, con promedio de 12% y rango entre 0 y 50%. La variabilidad del NASC Cp fue explicada significativamente por la profundidad del estrato integrado (33%), la condición climática medida por la escala de Beaufort (5%) y por el curso del barco en relación con la dirección del viento (2%). El modelo empírico construido para explicar la variabilidad observada posee un potencial uso predictivo para corregir el sesgo debido al movimiento del transductor en otras evaluaciones acústicas, pasadas y futuras, de recursos mesopelágicos y demersales bajo condiciones meteorológicas difíciles.

The fundamental parameters approach is used to simulate the instrument contribution to the X-Ray diffraction profile. This procedure eliminates the need to experimentally prepare a reference sample of the studied crystalline material when using the Warren-Averbach method to investigate microstrutural parameters. The Warren-Averbach method is also compared to the Balzar and Enzo methods, two other popular methods of size-strain analysis. The analysis was carried out using bohmite powder having two different nominal average crystallite sizes, 80 Å and 200 Å. A 50%-50% mixture of these materials was used as a third sample. The proposed simulation procedure provides good results and is much faster to implement than the usual procedure that includes the preparation of a reference. For larger crystallite sizes, the results calculated from the Warren-Averbach method for the volume-weighted average crystallite size differs significantly from the ones obtained from the Balzar and Enzo methods. The limitations of the Balzar and Enzo methods are also discussed.